Talking heads are the documentarian's device, and the long-hidden heads in Dror Moreh's "The Gatekeepers" have never talked before. They're the six extant former heads of Shin Bet, Israel's internal security agency charged with top secret antiterrorist activities and the intricate web of operatives required to carry them out.

It's fascinating just to see and hear these legendary hard-liners speak publicly and candidly, for the first time, about the bloody successes and failures of their tenures. Even more fascinating, and disturbing, is their unanimous conclusion about the mission.

Director Moreh gained inside access for his previous documentary "Sharon," which chronicled that Israeli prime minister's decision to disengage from Gaza. This time, he has achieved a far greater journalistic coup with the collective cooperation of the ex-spy chiefs, including Ami Ayalon, the country's most beloved Navy war-hero commando, and Avraham Shalom, a member of the team that tracked down and kidnapped Adolf Eichmann in Argentina and an early champion of Shin Bet's controversial license to kill.

"Forget about morality," he says in response to one of Mr. Moreh's questions. "It's not a moral decision, it's a tactical one."

Ex-chief Avi Dichter -- despite his more humanist perspective as an expert on Palestinian society -- largely echoes that view. He was a seminal advocate of "targeted assassination," several of which are provided here from aerial surveillance footage. "There's something unnatural about it -- to take three lives," he says softly, as we watch in stunned agreement.

Similar footage shows the elimination of a radical Islamic cleric by dropping a one-ton bomb on his house in a crowded neighborhood, then switching from air to ground level for review of the appalling civilian results. When an American criticizes the action, the Israeli official responds, "You killed 70 people at a wedding in Afghanistan."

Ex-chief Carmi Gillon justifies "enhanced interrogations" and speaks of switching Shin Bet's focus from Palestinians to the Jewish Underground's right-wing terrorism in the wake of the Oslo Accords. Mr. Gillon thwarted that group's attempt to blow up the Moslem Dome of the Rock (in order to provoke Armageddon -- a final total war of all Arab states against Israel!). But he speaks also of his tragic failure to prevent the assassination of conciliatory Prime Minister Yitzhak Rabin by a Jewish religious extremist in 1995 -- an act that more or less derailed the peace process and progress toward a two-state solution.

Mr. Moreh's unprecedented access to the inner sanctum's decision-making process is as stunning, in this Oscar-nominated documentary, as Errol Morris' in "The Fog of War: Eleven Lessons From the Life of Robert McNamara" (2003), an award-winning expose of the moral complexities and insanities of the Vietnam War, containing McNamara's chilling lament, "I was wrong! My God, I was wrong."

The Israeli spy chiefs, for their part, differ on some issues (such as the efficacy of targeted assassinations) but agree on the bottom-line results: The post-1967 occupation -- placing an additional million Palestinians under Israeli rule -- has been disastrous. "There were many times when we should have reached an agreement and gotten out," one of them admits. All of them have pessimistic contempt for Israeli politicians (except the murdered Rabin), consumed by tactics instead of strategy. All of them see peace slipping away and largely blame the incitement of extremist rabbis and their political enablers.

Mr. Moreh's "Gatekeepers" has a cliched, ominous soundtrack and too many annoyingly hi-tech, computer-generated graphic adornments. But it's a revelatory and provocative piece of investigative journalism and no-nonsense history of the Israeli-Palestinian conflict in pragmatic rather than ideological terms.

It is also a powerfully implicit -- not didactic -- polemic for a two-state solution and a "must-see" for those who care about Israel. No bleeding-heart liberal doves here, no blustering hawks, no outside "expert commentators." Just a painful dose of reality from the horses' mouths -- who spent their lives in Israel's dangerous service and understand the conflict best. If you don't believe them, who would you believe?

"F-16s versus suicide bombers ... ." It's been a horribly even match for decades. Balance of terror, balance of error in a mentally unbalanced cycle of violence, devoid of leadership on both sides.

"We win every battle," says one of the spy chiefs, "and we're losing the war."

In Hebrew and English, with English subtitles. Opens today at the Manor Theater in Squirrel Hill.